Is it reasonable to be pissed off with lateness, even though late people do me favours?

Relative was an hour later than she said she would be today when bringing her friend to visit my new baby. This annoyed me. However, do I have the right to be annoyed when she does me massive favours (childcare) and brings me food?

I hate lateness of any kind. But, to be uncharacteristically balanced, if you are at home with a newborn and no plans for the day then you could probably cut her some slack. As long as she called/text to warn you of impending lateness. Maybe. Depends what food too?